concurrency: re-export futures-concurrency?

[pchickey]

We believe tasks are the wrong abstaction. Lets instead make it as easy as possible for wstd users to use the right abstraction by re-exporting futures-concurrency, @yoshuawuyts 's crate that provides the right abstraction, and use it in wstd's examples and docs.

[pchickey]

Right now the thinking is we will re-export all of the modules from futures-concurrency except for prelude, and define a pub mod prelude { pub use futures_concurrency::prelude::*; pub use crate::io::{AsyncRead, AsyncWrite}, etc etc }

[pchickey]

We added tasks in #86.

[teohhanhui]

We believe tasks are the wrong abstaction.

Has this changed?

[pchickey]

At least personally I'd change my feelings to "tasks are the abstraction of last resort" rather than always wrong, but the broader ecosystem more or less demands tasks, and component model async has tasks. So, we relented.

[yoshuawuyts]

but the broader ecosystem more or less demands tasks

To expand on this: we want to be able to support Axum and Hyper on wstd, and both of these assume a particular task model. While I still hold that the tasks model is wrong, creating practical software now is more important than ideological purity.